Battery pack comprising heat-diffusing means

ABSTRACT

A pronounced heat-diffusing action for a battery pack, which has a plurality of battery cells ( 2 ) located in a housing ( 1 ), is created by shaping the wall of the housing ( 1 ) surrounding the battery cells ( 2 ) such that this wall forms at least one duct ( 3, 4 ) for a heat-diffusing medium, which duct is closed off from the interior of the housing ( 1 ).

CROSS-REFERENCE TO A RELATED APPLICATION

The invention described and claimed hereinbelow is also described inGerman Patent Application DE 10338654.8 filed on Aug. 22, 2003. ThisGerman Patent Application, whose subject matter is incorporated here byreference, provides the basis for a claim of priority of invention under35 U.S.C. 119(a)-(d).

BACKGROUND OF THE INVENTION

The present invention relates to a battery pack comprisingheat-diffusing means from a plurality of battery cells located in ahousing.

Rechargeable battery packs are used for operating power tools, forinstance. Both during the operation of a battery pack, or in other wordsduring its discharging process, and in the charging process, thecurrents flowing through the battery cells cause severe heating up ofthe battery cells. So that in the charging process the temperature ofthe battery cells will not exceed a maximum allowable threshold—whichwould lead to destruction of the battery cells—the charging current mustbe reduced, with the consequence that the charging time for the batterypack is lengthened. If a higher charging current and accordingly ashorter charging time for the battery pack are to be attained, excessiveheating of the battery pack must be avoided. In the prior art, measuresare therefore taken to diffuse heat of the battery cells from thebattery pack. For instance, in European Patent Disclosure EP 940 864 B1, a ventilation system for the battery pack is provided for thispurpose; it allows air to flow through the interior of the housing ofthe battery pack. To that end, air inlet and air outlet openings areprovided in the battery pack housing. A disadvantage is that with theflow of air through the housing of the battery pack, dirt particles canalso get into the interior of the battery pack. Soiling in the interiorof the battery pack, however, can change heat transfers among batterycells and can also impair the electrical function of the battery pack.The parts located in the interior of the battery pack form a high airresistance, which impairs the effectiveness of the heat diffusion.

SUMMARY OF THE INVENTION

The object of the invention is to disclose a battery pack withheat-diffusing means, which have the greatest possible heat-diffusingaction and moreover do not impair the function of the battery pack.

This object is attained in that the wall of the housing surrounding thebattery cells is shaped such that it forms at least one duct, which isclosed off from the interior of the housing, for a heat-diffusingmedium. According to the invention, the heat-diffusing medium is notcarried through the interior of the battery pack housing. This preventsdirt from getting into the interior of the battery pack and being ableto impair its electrical function. Moreover, the ducts, which arepartitioned off from the interior of the battery pack, form only a veryslight flow resistance to the heat-diffusing medium flooding through,and the result is a strong cooling action.

The heat diffusion can be optimized in that the at least one duct isshaped such that its wall rests in form-locking fashion against thebattery cells adjacent to it. An especially high heat diffusion becomespossible because the wall regions that form the at least one duct atleast partly comprise a heat-conducting material.

It is expedient for the wall regions of the at least one duct thatcomprise a heat-conducting material to be recessed so far from the outerwall regions of the housing that contact with the heat-conductingmaterial by a user is prevented.

The invention is described in further detail in terms of a plurality ofexemplary embodiments shown in the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

-   -   FIG. 1, a plan view on a battery pack with battery cells located        in it;    -   FIG. 2, a cross section A-A through the battery pack, in which        the duct for the heat-diffusing medium is a separate part        inserted into the housing; and    -   FIG. 3, a cross section through a battery pack in which the duct        is formed by two housing parts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a plan view on a battery pack, in which a plurality ofcylindrical battery cells 2 are located in a housing 1. In a position ofthe battery pack shown, the longitudinal axes of the cylindrical batterycells 2 extend perpendicular to the plane of the drawing.

In the exemplary embodiment shown in FIG. 1, the housing 1 is providedwith two ducts 3 and 4, through which a heat-diffusing medium, such asair, can be passed. It is also possible for only one duct or for morethan two ducts to be provided. The ducts 3 and 4 are formed by suitableshaping of the housing 1 of the battery pack such that they arecompletely closed off from the interior of the housing 1. Thus aheat-diffusing medium passed through the ducts 3 and 4 cannot get intothe interior of the battery pack, and consequently no dirt particles canget into the housing along with the heat-diffusing medium. The smoothwall of the ducts 3 and 4 assures a fluidically favorable guidance ofthe heat-diffusing medium, which leads to a very good cooling action.The transporting of the heat-diffusing medium can be done by naturalconvection, or by means of convection reinforced with a blower. Such ablower may for instance be a component of the battery pack or of thecharger for the battery pack, or of the machine into which the batterypack is inserted.

As the cross section A-A through the battery pack in FIG. 2 also shows,the ducts 3, 4 extend parallel to the longitudinal axes of thecylindrical battery cells 2. This location of the ducts 3 and 4 isespecially favorable because the ducts 3 and 4 are located in the nipsbetween the individual battery cells 2. This has the advantage that thewalls 5 and 6 of the ducts 3 and 4 can be brought into heat-conductingcontact with the adjacent battery cells 2 over a large area. However,the ducts may also be located transversely or diagonally to the batterycells and may also have cured courses. As can be seen particularly fromFIG. 1, the walls 5 and 6 of the ducts 3 and 4 are preferably shapedsuch that they rest by form-locking on the battery cells 2 adjacent tothem. If the walls 5 and 6 of the ducts 3 and 4 comprise an especiallyhighly heat-conducting material (such as metal), the heat diffusionaction is especially pronounced.

In the exemplary embodiment shown in FIG. 2, the housing 1 of thebattery pack comprises an upper housing shell 11 and a lower housingshell 12. The walls 5 and 6 of the ducts 3 and 4, respectively, areformed by respective parts 5, 6 inserted between the two housing shells11 and 12. As the exemplary embodiment in FIG. 2 shows, these housingparts 5, 6 are recessed relative to the upper housing shell 11 and lowerhousing shell 12, so that contact by a user with the especially highlyheat-conducting material of the walls 5 and 6 is prevented.

In a further exemplary embodiment, shown in FIG. 3, the walls of theducts 3, 4 are formed directly onto the housing shells 11, 12.

1. A battery pack, comprising a housing forming only one compartment; aplurality of battery cells located in said one compartment of saidhousing and having longitudinal axes; and heat-diffusing means fordiffusing heat from said battery cells, said heat diffusing meansincluding a wall of said housing which is peripherally adjacent to saidbattery cells from outside of said battery cells and is shaped so thatit forms at least one peripherally closed and uninterrupted duct whichextends parallel to said longitudinal axes of said battery cells fromone axial side to another side of said housing, is open outside at saidone and another axial sides, and is closed off in its entirety from saidone compartment of said housing in which said battery cells are located,for passing a heat-diffusing medium, wherein said at least one duct islocated in a nip between individual ones of said battery cells and haswall regions that rest in form-locking fashion against said batterycells that are located adjacent to said wall regions.
 2. A battery packas defined in claim 1, wherein said wall regions of said at least oneduct include at least partly a heat-conducting material.
 3. A batterypack as defined in claim 2, wherein said wall regions of said at leastone duct that include said heat-conducting material are recessed so farfrom outer wall regions of said housing that contact with saidheat-conducting material by a user is prevented.
 4. A battery pack,comprising a housing forming only one compartment; a plurality ofbattery cells located in said one compartment of said housing and havinglongitudinal axes; and heat-diffusing means for diffusing heat from saidbattery cells, said heat diffusing means including a wall of saidhousing which is peripherally adjacent to said battery cells fromoutside of said battery cells and is shaped so that it forms at leastone peripherally closed and uninterrupted duct which is located betweenindividual ones of said battery cells from one axial side to anotheraxial side of said housing, extends parallel to said longitudinal axesof said battery cells, is open outside at said one and another axialsides, and is closed off in its entirety from the said one compartmentof said housing in which said battery cells are located, for passing ofa heat-diffusing medium from one axial side to another axial side ofsaid housing between said battery cells, wherein said at least one ductis located in a nip between individual ones of said battery cells andhas wall regions that rest in form-locking fashion against said batterycells that are located adjacent to said wall regions.
 5. A battery pack,comprising a housing forming only one compartment; a plurality ofbattery cells located in said one compartment of said housing and havinglongitudinal axes; and heat-diffusing means for diffusing heat from saidbattery cells, said heat diffusing means including a wall of saidhousing which is peripherally adjacent to said battery cells fromoutside of said battery cells and is shaped so that it forms at leastone peripherally closed and uninterrupted duct which is located betweena plurality of individual ones of said battery cells, extends parallelto said longitudinal axes of said battery cells, is open outside at saidone and another axial sides, and is closed off in its entirety from saidone opening of said housing in which said battery cells are located, forpassing of a heat-diffusing medium from one axial side to another axialside of said housing between said battery cells, wherein said at leastone duct is located in a nip between individual ones of said batterycells and has wall regions that rest in form-locking fashion againstsaid battery cells that are located adjacent to said wall regions.